This invention relates to barrier wire which can be used for deterrent purposes.
Razor wire, a typical example of barrier wire, includes a high tensile steel core to which a deterrent strip, formed with a plurality of sharp spikes, is secured. This construction, when properly utilised and configured, can present a formidable physical barrier to a would-be intruder.
It is, nonetheless, possible for an intruder to sever razor wire using bolt cutters or the like. This negates the physical effect of the barrier. To counter this type of action it is possible to include a signal wire in the razor wire. If the signal wire is severed an alarm will be sounded. The inclusion of the signal wire does however present certain technical problems.
In most countries, it is not legally permitted to electrify razor wire, or a similar barrier which has a “snagging” effect. If an intruder becomes trapped by electrified razor wire, the intruder may be fatally injured. If a signal wire is used, i.e. a conductor which can operate at a low voltage and current, then some means must be found of insulating the signal wire from the deterrent strip. If the signal wire is used as a direct replacement for the high tensile core wire then, unfortunately, the physical strength of the razor wire is adversely affected to the extent that an intruder can usually simply flatten or push the razor wire aside. On the other hand if a high tensile core wire is insulated then, when the deterrent strip material is crimped onto the core wire, it is not possible to guarantee that the integrity of the insulation will remain unscathed. The crimping force is often so high that the insulation is compressed and can break, and the insulating strip can then contact the core wire. This manifests itself as a short circuit and the capability of this type of razor wire to function as a sensor, which detects severance of the razor wire, is then rendered valueless.
The last-mentioned problem can be overcome, to some extent, by forming the core wire with a robust, thick, insulating sheath. This however can be expensive for it calls for greater quantities of materials.
A different problem presents itself when the razor wire is to be used in a corrosive environment, for example near the sea. The strip which, typically, is made from a thin sheet of steel, is degraded fairly quickly. In order to have a reasonable lifetime the strip should be formed from a corrosion-resistant material such as aluminium. However, when this is done, electrolytic corrosion effects manifest themselves due to the core wire and strip being made from dissimilar metals which are in contact with each other. This phenomenon impacts adversely on the core wire and the strip.
G82300206 discloses an insulating sheath around a conductor but there is no solution mentioned in the specification which addresses the problem of damage which could be caused to the insulating sheath.
U.S. Pat. No. 4,509,726 deals with conventional barbed tape wherein a core wire is noy insulated.
EP0073927 discloses a configuration in which an insulated core is used but with a segmented deterrent strip material.
An object of the present invention is to provide barrier wire which allows for the use of dissimilar metals and wherein the insulating sheath on a core wire its protected.